Bioactivity testing for the chemical compounds whether natural, semisynthetic or synthetic and monitoring environment for the presence of physical stress factors and hazards like radioactivity, radiation and temperature shocks have been a major concern for all those who are concerned about the environment for the following main reasons:                Monitoring the compounds for their toxicity or pollution hazards before they are permitted to be released into any practical use in the environment.        Bioevaluating the compounds for their potentials in developing drugs or agrochemicals        Biosensing the presence of physical extremities in the environment which could amount to physical damage/shock to the organisms living there.        
The emphasis in the present day scenario is centered on natural compounds not only for their direct use but also for providing the biorational leads in developing semisynthetic compounds with higher efficacy. These biorational leads are expected to be more biocompatible and therefore the appropriate tests have to be applied for both positive and negative effects. About 51 tests are well known to be approved for the use within OECD countries (Organization for Economic Co-operation and Development: Guidelines for Testing of Chemicals. OECD, Paris, 1981, for testing of chemical compounds. Some of the higher plant species have also been used for toxicity assessment of industrial wastewater including common duckweed (Lemna minor), lettuce, rice (Oryza sativa) and wheat etc. Wang W, 1990, Res. J. Water Pollut. Con. Fed. 62: 853–860; Wang W, 1991, Plants for Toxicity Assessment, second volume, J W Gorsuch, W R Lower, W Wang and M A Lewis, Eds. ASTM STP 1115, American Society for Testing and Materials, Philadelphia, pp 68–70). A single test has never been advocated as sufficient enough to be employed as biotesting procedure particularly, when the compound under question is to be evaluated for environmental toxicity/hazard (Fiskesjo G, 1982, Ph.D. Thesis, Institute of Genetics, University of Lund, Sweden).
In addition, use of a battery of tests rather than any single test in isolation has also been preferred to reduce the possibility of false negative and false positive results (de Serres, 1976, Mutation Research, 38: 165–176 and 355–358). In fact, this opinion has always been the general consensus among the regulatory agencies as well (Committee 17, 1975, Science, 187:503–514). Availability of several tests has resulted into their broad classification among four main classes (Maugh, 1978 Science, 201:1200–1205). These include:                The tests with micro-organisms.        The tests with intact organisms.        The tests with cultured/mammalian cells.        The tests for in-vitro activities.        
In the above categories, for the tests with intact organism, a very popular root tip assay system using Alliuin ceua sprouted bulbs was introduced by Levan 1938, while investigating the effects of colchioine. The usefulness of plant system in tests of chemicals even those which need metabolic activation has been emphasized (Vig B K, 1978, Environment Health Perspect. 27: 27–36) for the preliminary screening of new chemicals being introduced into the environment. The Allium test has also been listed as a short term procedure for the detection of chemical carcinogens (Stich H F, 1975, Can. J. Genet. Cytol. 17:471–492). The positive results in these tests have been suggested to be considered as a warning that the tested chemicals may be a risk to human health. The first attempt to approach the problem of genotoxical effect of environmental chemicals was on a commercial fungicide (called Be Toxin) containing mercury compounds (Levan A, 1945, Nature, 156:751). Subsequent studies on effect of mercury halogenides in Allium tests have substantiated the confirmation with compounds like methyl mercury chloride (MMC) and ethyl mercury chloride (EMC) etc. (Levan A, 195 1, C.S.H. Symp. Quant. Biol. 16:233–243; Fahmy F Y, 1951, Ph.D. thesis, Inst.Genet., Lund, Sweden; and Remel, C. 1969, Hereditas 61:208–230). The original form of test wherein outgrowth of root tips from onion bulbs in fresh water which was followed by treatment with test chemical solution has undergone several modifications to have several replicates together (Fiskesjo G, 1975, Vatten 31(4):304–316 and Fiskesjo G, 1981, Vatten 37(3):232–240).
The system, although very useful to study the responses of a variety of cell division inhibiting substances, has certain inbuilt limitations which are as follows:                The parameters which can be studied using this test procedure are mainly confined to cytological observations including cell division.        This test is not usable for assessing the growth promotion activities since the responses are observed only in the root tips and thus do not take into consideration the effects on aerial parts of the plant as a direct measure.        It requires independent onion bulbs in the sprouting stage for each treatment of every replication which amounts to large bulk of starting material and becomes impractical when thousands of samples are to be tested.        The root sprouting of bulbs is not possible throughout the year under ambient condition and therefore the experiment would require storing the right stage of bulb under controlled conditions.        Each bulb has to be sprouted on top of a tube/flask filled with buffer having minimum 15×20 mm diameter and therefore requires large volumes of buffer or medium for testing the compounds.        